1. Field of Art
This invention relates to a method for the recovery and purification of palladium. More particularly, this invention relates to a novel method of recovering and purifying palladium through use of ortho alkoxy substituted phenyl oxime compounds which are capable of selectively separating and recovering palladium from aqueous compositions and mixtures containing palladium and other metal ions such as aluminum, nickel, iron, copper, platinum, rhodium, ruthenium and the like.
2. Prior Art
The recovery and purification of platinum group metals, such as palladium and platinum, are important commercial processes. Such processes are useful in the recovery of palladium from solutions obtained in the recovery of mineral deposits of the platinum metals which solutions commonly contain in addition to palladium, ruthenium, rhodium, iridium, platinum, aluminum, iron, and nickel. Such processes are also useful in the recovery of palladium from spent catalyst materials, such as materials obtained from automobile catalytic converters.
Several extraction methods have been developed for recovery of metal values. Solvent extraction processes for the recovery of metal values have certain well recognized advantages over other recovery methods, and such solvent extraction processes are increasing in number and types of applications. Fundamental to a successful solvent extraction process for the recovery of a platinum group metal such as palladium, is the identification of a water immiscible composition, (combination of compounds which will selectively bind to the metal and a solvent) which will selectively extract one platinum group metal from an aqueous solution containing the platinum group metal and other metals. A further requirement for a successful metals recovery by solvent extraction techniques is an extracting composition having the property such that metal values extracted by the extracting solvent can be recovered from same using another suitable aqueous phase.
Illustrative of such prior art solvent extraction methods are those described in U.S. Pat. No. 3,967,956 and United Kingdom Pat. No. 2,013,644. In the processes of these patents, palladium is recovered from a mixture of palladium and other platinum group metals through use of an extracting composition containing ortho hydroxy oxime compounds, such as alkyl substituted ortho-hydroxyphenyl oxime compounds. The extracted palladium metal is removed from the extracting composition by contacting same with a strong acid solution. This method is generally a useful procedure for recovering certain metals from the extracting composition because this recovery is pH dependent. With ortho-hydroxy phenyl oximes, the extraction process is dependent on the ionizable nature of the phenolic hydrogen, and in the Cu.sup.+2 system is generally believed to follow the following equilibrium in which "LH" is the un-ionized oxime: ##STR2##
Presumably, the Pd.sup.+2 system would operate in a similar manner when being extracted by orthohydroxy phenyl oxime compounds. In which case palladium values are extracted into the organic, water immiscible extracting composition as the neutral species "PdL.sub.2 ", while LH ionizes in the aqueous phase so that the acidity of the aqueous phase increases. Recovery by treatment with strong acid is effective because by shifting the equilibrium the oxime is protonated releasing the palladium as Pd.sup.+2 which migrates to the aqueous phase.